It's Always Sunny In Philadelphia: 10 Cameos You (Probably) Missed
1. Christopher Lloyd
He may have been hard to recognize since he was wearing a Santa costume with a fake beard, but Christopher Lloyd appeared in Season 6, Episode 13, "A Very Sunny Christmas." He plays one of the Santas that visit Charlie's house in a childhood flashback, where Charlie realizes that his mother was a Christmas prostitute. Charlie then releases his anger on a poor mall Santa.
Charlie Lloyd is most famous for playing the iconic role of Doc in Back to the Future. He also appeared in Who Framed Roger Rabbit, Clue, and Addams Family Values.